The overall objective of this proposal is to define the essential molecular mechanisms that underlie the role of COUP-TFII in the regulation of endometrial function in preparation of the uterus to support pregnancy and how alteration of these mechanisms results in endometrial dysfunction, such as endometriosis. During the last funding period, we have demonstrated, using genetically engineered mouse models, that COUP-TFII is critical in regulating the initiation of pregnancy by controlling the ability of the uterus to support embryo attachment, invasion, and the maintenance of pregnancy. COUP-TFII regulates these processes by controlling uterine epithelial cell sensitivity to estrogen, as well as, uterine stromal cell proliferation, vascularization, and differentiation by regulating Wnt and Epidermal Growth Factor (EGF) signaling pathways. Using primary human endometrial tissue, we have shown that this pathway is conserved in the human endometrium and COUP-TFII is critical for the ability of human endometrial stromal cells to differentiate in vitro. The goal of this proposal will be to investigate how COUP-TFII regulates endometrial epithelial ER signaling and stromal Wnt and EGFR signaling in the regulation of endometrial function and dysfunction. This will be accomplished by achieving the following aims: 1 .The importance of COUP-TFII regulation of endometrial epithelial E2 sensitivity in controlling uterine receptivity will be investigated. 2. The role of COUP-TFII in the regulation of human endometrial estrogen sensitivity will be determined. 3. The molecular mechanism by which COUP-TFII regulates the expression of target genes in human endometrial stromal cells will be investigated. 4. The role of EGFR in the ability of the PR-lhh-COUP-TFII axis to regulate endometrial function will be investigated. Accomplishment of these aims will define the molecular mechanisms regulating endometrial function and dysfunction.